For the past month, CNN has conducted a state-by-state survey to determine enrollment in the new insurance plans. As of Tuesday afternoon, at least 133,257 people had chosen new insurance plans in the 14 states with their own signup apparatuses. Nearly half of them were enrolled in the past two weeks.

One of the biggest jumps is in California. Through November 2, 35,364 Californians had selected private plans through the new insurance marketplace. Less than two weeks later, the number was up to 59,000. The state with the second-highest enrollment is New York, where at least 24,509 have selected a plan. The next highest enrollments are in Washington state, Kentucky and Connecticut.

Enrollment is harder to pin down in the 36 states using HealthCare.gov, although it's running well behind the states with their own programs. As of November 2, just 26,794 people had enrolled in the HealthCare.gov states. CNN's current tally for this group is 43,743 enrollees, but that's based on just a handful of states that have provided updates.

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In addition, 58,857 newly eligible people have enrolled in state Medicaid programs, with another 275,131 people signed up to start Medicaid coverage on January 1, 2014.

Young, healthy needed

Aside from raw enrollment numbers, the data are being scrutinized for any hints about the makeup of the newly insured.

In its projections, the Congressional Budget Office estimated that 7 million people would enroll in private insurance plans through the marketplaces in 2014, and that 2.7 million -- about 38% of the total -- would be between the ages of 18 and 34.

"There's general agreement that we need younger and healthier people to offset the costs of sicker people coming into the system," says Robert Zirkelbach, a spokesman for America's Health Insurance Plans, an industry group. "That's what will add more stability."

If the concentration of older and sicker enrollees in the new plans is too high, insurers could be forced to raise their rates, which would further discourage young and healthy people from signing up. Taken to an extreme, this vicious cycle could -- in theory -- lead to what Obamacare critics call a "death spiral" and the collapse of the law.

Industry spokesman: Too early to draw conclusions

So, how's it going?

It's a limited picture. HHS hasn't released demographic data for people signing up through HealthCare.gov, and only three states provided their own data to CNN. In those states, the number of under-35 enrollees is less than CBO projected: in Kentucky, 19% of enrollees are age 18-34. In Connecticut and Washington state, the figures are 22% and 23%, respectively.

But Zirkelbach says it's way too early to draw conclusions. "There's lots of evidence to suggest that people needing serious medical care are most likely to purchase insurance initially. Those who don't have urgent medical needs are more likely to purchase insurance later."

What's more, age is only a piece of the puzzle. Since those applying for insurance no longer disclose anything about their health, Zirkelbach says insurers won't have a good sense of their medical needs -- and what it will cost to cover them -- until well into 2014.

Obamacare architect: No risk of a 'death spiral'

The law's supporters say the dire scenarios are farfetched.

"There is essentially no risk of a 'death spiral,'" says MIT economist Jonathan Gruber, who helped design the ACA as well as the Massachusetts law on which it was modeled. "There are substantial risk mitigation mechanisms as well as subsidies that will attract in healthy enrollees." Most important, say Gruber and Zirkelbach, is a section of the ACA under which the federal government will pick up a substantial portion of the losses for the next three years, if the program goes sour for insurers.

There's no precedent for a program of this size and scale, and Gruber warns that that the early data are ripe for overinterpretation. While fewer young and healthy customers would mean higher premiums, "it's hard to say how big a difference 28% vs. 38% makes -- we just don't know."

The trends are likely to come into sharper focus in the next several weeks. Most experts expect the pace of enrollment to accelerate, as the HealthCare.gov website starts to function better and potential customers have more of a chance to explore their options.

So far, by CNN's count nearly 900,000 people have completed applications for new insurance but have not yet selected a plan.